Remove nullable boolean "idiom"

[SebastianAigner]

Open for discussion here @JetBrains/kotlin-technical-writing – I don't understand the original motivation for adding this as a Kotlin "idiom", seeing how this seems like an instance of the tri-state boolean problem.

If there is a reason as to why we're highlighting this as an idiom, I'd appreciate a short explanation – otherwise, it's probably better if it is removed.

[koshachy]

Hey @SebastianAigner
Thanks for raising the issue!
This idiom was added long ago, and I can't find any reason why it should be in the documentation.

I agree with you that we should remove it.
Thanks again for pointing this out!
We appreciate it!

[YSakhno]

Frankly speaking, I do not understand why this was removed. This idiom, as it was written, while very trivial, is not obvious. As in, it's hard to come up with it on your own — when someone unfamiliar with the "idom" is hard pressed to use nullable Boolean in an "if" (or otherwise convert nullable Boolean to a non-nullable one), they will most likely write b!! or b ?: false. To me, if (b == true) is more idiomatic than if (b ?: false) (and much, much more idiomatic than if (b!!)).

If your argument was "simply don't use nullable Booleans", then why is it in the language at all? Sometimes you have to use it because it is more convenient, or because such are the constraints of the underlying system.

P.S. I would actually extend this idiom by including the case of defaulting null to true: b != false (although this might be less obvious to the reader than b ?: true).

P.P.S. Also see Detekt's NullableBooleanCheck. Your change will break their rules, because they are referencing the very much idiom you removed.